Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design;

FIG. 2 is the second image thereof;

FIG. 3 is the third image thereof; and,

FIG. 4 is the fourth image thereof.

The appearance of the graphical user interface transitions between the images shown in FIGS. 1-4. The process or period in which one image transitions to another forms no part of the claimed design. The broken line showing of the text and the remainder of the graphical user interface illustrates portions of the graphical user interface and forms no part of the claimed design. The outermost broken line showing of the remainder of the display screen illustrates environmental structure and forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 